Pegmatites of Shangfu deposits, Lianyunshan, northeastern Hunan: Geochemical characteristics, fluid inclusions, and genetic constraints

doi:10.13745/j.esf.sf.2023.5.7

Abstract

Abstract:

The recent discovery of the Nb/Ta-rich, No.3 pegmatite vein in Shangfu area, Lianyunshan intrusion, northeastern Hunan, shows a good prospect for rare-metal deposits in this area. In this paper, the geochemistry of the Shangfu pegmatite and fluid inclusions in host minerals are studied, and the genesis of the pegmatite deposit is discussed to enrich the understanding of rare-metal mineralization in the region. The Shangfu pegmatite is characterized by high silicon (w(SiO₂), 65.05%-79.15%), high aluminum (w(Al₂O₃), 11.38%-19.64%) and low Ca, Mg, Fe contents, and is relatively rich in alkali (w(Na₂O+K₂O), 5.62%-9.87%), (medium potassium) calc alkaline and peraluminous. The pegmatite is distinctively enriched in Nb, Ta, Zr, Hf and U, and relatively depleted in Ba and Sr; ∑REE ranges between (11.74-29.40)×10^-6, with enriched LREE and depleted HREE, consistent with a crustal origin. The fluid inclusion type is gas-liquid two-phase brine solution; the homogenization temperature of the fluid inclusions is between 159-443 ℃; the salinity of brine solution is 3.06%-6.74%; and the average trapping pressure of the fluid inclusions is 190 MPa. The ore-forming fluid is characterized by medium-high temperature and low salinity; and C, H, O isotopic analysis shows that the ore-forming fluid is related to deep magmatic activity and may be mixed with a small amount of formation water. The rare-metal mineralization is controlled by magmatic differentiation and evolution. The mica monzonitic granite and pegmatite in the area have the same material source which provides the source material and ore-forming fluid responsible for Nb/Ta mineralization.

Key words: geochemistry, ore-forming fluid, fluid inclusion, Shangfu pegmatite, Lianyunshan

CLC Number:

HUANG Xiaoqiang, LIU Qingqi, LI Peng, LIU Xiang, ZENG Le, ZHANG Liping, SHI Weike, HUANG Zhibiao, FAN Pengfei, WAN Haihui, LIN Yue, WANG Xuanmin, CAI Chang. Pegmatites of Shangfu deposits, Lianyunshan, northeastern Hunan: Geochemical characteristics, fluid inclusions, and genetic constraints[J]. Earth Science Frontiers, 2023, 30(5): 298-313.

Figures/Tables 16

Fig.1 Geological and mineral resource map of Lianyunshan. Adapted from [24].

Fig.2 Geological sketch map of the Shangfu deposit

Fig.3 (a, b) Outcropping of and (c) internal zonation in No.3 pegmatite vein

Fig.4 Macro and microscopic features of the Shangfu pegmatite

Table 1 Whole-rock analysis outline

样品号	岩性	分析测试项目	脉体编号
SF-WJY1-H01	中粗粒钠长石伟晶岩	岩矿鉴定,主量、微量、稀土元素测试,流体包裹体测温、激光拉曼及C-H-O同位素分析	γρ₃
SF-WJY1-H02	中粒含石榴子石白云母钠长石伟晶岩	岩矿鉴定,主量、微量、稀土元素测试	γρ₃
SF-WJY2-H01	中粗粒白云母钠长石伟晶岩	主量、微量、稀土元素测试	γρ₃
SF-WJY2-H02	中粗粒白云母钠长石伟晶岩	主量、微量、稀土元素测试,流体包裹体测温、激光拉曼及C-H-O同位素分析	γρ₃
SF-WJY3-H01	微斜长石伟晶岩	岩矿鉴定,主量、微量、稀土元素测试	γρ₂
QHD-HP-H01	片岩	岩矿鉴定,主量、微量、稀土元素测试
TLW-HGY-H01	中粒似斑状二云母花岗岩	主量、微量、稀土元素测试

Table 2 Results of whole-rock major element analysis of the Shangfu pegmatite

Fig.5 (a) SiO2-K2O (after [26]) and (b) A/CNK-A/NK (after [27])plots for the Shangfu pegmatite (Granite-2 data from [1])

Table 3 Results of trace element analysis of the Shangfu pegmatite

Fig.6 (a) Primitive mantle-normalized trace element pattern and (b) chondrite-nomalized REE pattern of the Shangfu pegmatite. Normalization values are from [28]; granite data from [1].

Fig.7 Fluid inclusions in quartz from the Shangfu pegmatite vein

Table 4 Properties of primary fluid inclusions in the Shangfu pegmatite

包裹体类型	宿主矿物	观测的包裹体个数	均一温度/℃	冰点温度/℃	盐度(w(NaCl))/%
气液两相包裹体	SF-WJY-H01石英	20	203~443	-1.8~-4.2	3.06~6.74
气液两相包裹体	SF-WJY-H02石英	11	159~306	-2.0~-3.6	3.39~5.86

Fig.8 Histograms of homogeneous temperature (a) and salinity (b) of fluid inclusions

Fig.9 Estimation of capturing pressure of brine inclusions. Modified after [30].

Fig.10 Raman spectra of fluid inclusions in quartz from the Shangfu deposit

Table 5 Isotopic compositions (H, O, C) of aqueous inclusions and hosting quartz

样品号	矿物	δD_V-SMOW/‰	δ¹⁸O_V-PDB/‰	δ¹⁸O_V-SMOW/‰	δ¹⁸ $O H 2 O - S M O W$ /‰	δ¹³C_V-PDB/‰
SF-WJY1-H01	石英	-64.5	-14.5	15.9	7.6	-9.8
SF-WJY1-H02	石英	-62.5	-15.8	14.6	6.3	-13.3

Table 5 Isotopic compositions (H, O, C) of aqueous inclusions and hosting quartz

样品号	矿物	δD_V-SMOW/‰	δ¹⁸O_V-PDB/‰	δ¹⁸O_V-SMOW/‰	δ¹⁸ $O H 2 O - S M O W$ /‰	δ¹³C_V-PDB/‰
SF-WJY1-H01	石英	-64.5	-14.5	15.9	7.6	-9.8
SF-WJY1-H02	石英	-62.5	-15.8	14.6	6.3	-13.3

Fig.11 δD-δ18O plot for aqueous inclusions in quartz from the Shangfu deposit (basemap after [32])

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